1. Field of the Invention
The present invention relates to reconditioning ammonium-nitrate-containing radioactive filtrates such as are produced in the AUC (ammonium uranyl carbonate) or the AUPuC process.
2. Description of the Prior Art
In the AUC process, which is described in detail in German Published Non-Prosecuted Applications Nos. 195 24 77 and 159 24 71, filtrates are produced which have the following composition if uranyl nitrate was the starting product:
______________________________________ Approximately 100 g/1 NH.sub.4 " 150 g/1 NO.sub.3 " 90 g/1 CO.sub.3 " 300 mg/1 U ______________________________________
The filtrates from the AUPuC process are similar; the plutonium content is an added component.
If unirradiated and plutonium free uranyl nitrate is used as the starting product, the filtrate from the nuclear fuel production can be discharged into the sewer system after sufficient chemical separation of uranium and its decay products, without radiologically affecting the environment.
This is no longer possible, however, if irradiated uranium or plutonium is contained therein. Chemical decontamination is then no longer sufficient.
The filtrate volume coming from the nuclear fuel production is relatively large, so that it cannot be delivered to ultimate storage after solidification. It is necessary to find possibilities for reducing the volume to the greatest extent possible.
Complete evaporation is prohibited because of the danger of explosion which exists here because of the ammonium nitrate. However, the water must be separated from the radioactive components to reduce the volume; the ammonium nitrate must therefore be decomposed.
There are several methods for thermally decomposing this nitrate at temperatures above 250.degree. C., wherein the water is evaporated with the decomposition products. The radioactive components remain in the reaction vessel.
These methods have the disadvantage that they can decompose the filtrates only if they have first been boiled down to 75-80% NH.sub.4 NO.sub.3. The danger of an explosion cannot be precluded, however. In addition, the decomposition products generated cannot be recycled and can be reused only at great cost. The relatively high temperature level, in addition, makes these thermal processes relatively expensive. It should also be mentioned that the necessary cleaning of the equipment of the radioactive components (plutonium dust) is likewise a cause of problems.